Load current indicator including a transformer coupled
suppressed glow discharge device



June 28, 1966 K. MEYER 3,258,693

LOAD CURRENT INDICATOR INCLUDING A TRANSFORMER COUPLED SUPPRESSED GLOW DISCHARGE DEVICE Filed Oct. 29, 1962 16 so LOAD L 3 20 LOAD 115 OR 220 V 60% 7 115 v.' 15K 68K 15 I WNE-2H I 20 13 3500 TURNS g 2 I 22 M CURRENT RANGE 1 LOAD -z .3 T0 3.5 A 33 34 S 101/ TURNS 3g 1 5 LOAD iCURRETNoTzRaAliGE 1 /2 TURNS F I G 5 INVENTOR.

KENNETH MEYER ATTORNEY United States Patent 3,258,693 LOAD CURRENT INDICATOR INCLUDING A TRANSFORMER COUPLED SUPPRESSED GLOW DISCHARGE DEVICE Kenneth I. Meyer, Middlehury, Conn., assignor to Sperry Rand Corporation, Great Neck, N.Y., a corporation of Delaware Filed Oct. 29, 1962, Ser. No. 233,582 2 Claims. (Cl. 324122) The present invention relates to current indicating devices for indicating abnormal current flow through a portion of an electrical circuit, for example, usually through a load.

It is desirable in many instances to be able to determine whether the current flowing through a portion of a cir cuit or through a load is normal without interrupting the circuit or interferring with the operation of the load. Normally, devices of this nature includes relays or other mechanical devices which tend to stick or change their characteristics 'with age. This is not desirable since the current indicator may be operative for a long period of time without providing an indication of an abnormal condition, when when an abnormal condition does occur it is mandatory that it be indicated and corrected forthwith. It is also desirable to provide a current indicating device of this type which is reliable, compact and eliminates any moving parts. Further, it is desirable to provide a current indicator which provides a visible indication only upon abnormal operation of the circuit being monitored and at other times the current indicator is extinguished.

It is, therefore, an object of the present invention to provide a simple compact current indicating device which does not interfer with the circuit being tested.

It is a further object of the present invention to provide a current indicating device which provides a signal only upon abnormal operation of the circuit being monitored that includes no moving parts or elements having any appreciable change in characteristics with age.

The above objects are accomplished by the present invention by utilizing a glow discharge device having an alternating current excitation source which provides a potential in excess of the threshold potential of the glow discharge device. Another potential is developed which is representative of the current flowing through the load that is in phase opposition with the excitation potential of the glow discharge device and of suflicient potential to reduce the excitation potential of the glow discharge device below its threshold potential. Under normal operation, the excitation voltage and the opposition voltage effectively cancel each other thereby preventing the glow discharge device from firing. However, under abnormal conditions, the opposition voltage does not eifectively cancel the excitation voltage and the glow discharge device ignites thereby indicating abnormal operation of the portion of the circuit being monitored.

Referring to the drawings,

FIG. 1 is a schematic wiring diagram of a series version of the present invention,

FIG. 2 is a schematic wiring diagram of a parallel version of the present invention,

FIG. 3 is a schematic wiring diagram of an alternative embodiment of FIG. 2.

Referring to FIG. 1, a power source of a single phase alternating current is connected by leads 11 and 12 to provide current to a load 13 when the switch 14 is in a closed position, as indicated by the dotted lines. In many instances it is desirable to monitor the current flowing through the load 13 in order to determine whether the current supplied thereto is normal or otherwise. In order to accomplish this, a glow discharge device 15 Patented June 28, 1966 has one of its electrodes connected to the lead 11. Its other electrode is connected through a resistor 16 and the secondary winding 20 of a current transformer 21 to the lead 12. The primary winding 22 of the transformer 21 is connected to the load 13 and to the lead 12. A condenser 23 is connected across the secondary winding 20 to provide a phase shift correction in a manner to be explained.

In operation, with the switch 14 open, the power source 10 provides an excitation voltage to the glow discharge device 15 which is in excess of its ignition threshold voltage thereby causing the device 15 to ignite. How ever, during normal operation of the circuit, the switch 14 is closed and the current through the load 13 develops an opposition voltage by means of the current transformer 21. The turns ratio of the transformer 21 is arranged to provide a voltage in the secondardy winding 20 of the transformer 21 that is in phase opposition to the voltage coming directly from the source 10, and has an amplitude suflicient to reduce the excitation potential of the glow discharge device 15 below its threshold potential when opposing the excitation potential. Therefore, at the glow discharge device 15, the excitation voltage and the opposition voltage oppose and eliectively cancel each other thereby preventing the glow discharge device 15 from firing during normal operation.

During abnormal operation, the load 13 has an abnormal amount of current flowing therethrough which may, for example, include no current flowing therethrough in the event of an open in the load circuit. In this event, the voltage developed at the secondary winding 20 of the transformer 21 does not effectively cancel the excitation voltage across the glow discharge device 15. With its threshold voltage exceeded, the device 15 ignites thereby providing an indication of abnormal current flow through the load 13. With the embodiment shown in FIG. 1, the condenser 23 is necessary to provide the phase shift correction needed at the secondary winding 21) of the transformer 21.

The embodiment of the present invention shown in FIG. 2 has the advantage of bucking out potentials that are substantially less than the line voltage and also eliminates the necessity for the condenser 23. In FIGS. 2 and 3 the elements which are identical to FIG. 1 are indicated by identical reference numerals. In FIG. 2 the glow discharge device or lamp 15 is connected to the power source 10 through a voltage dividing means 24 consisting of resistors 25 and 26 and in parallel with respect to the secondary winding 20. In this embodiment, the voltages which are compared across the lamp 15 may be of substantially lower potential than those of the embodiment of FIG. 1 thereby utilizing less power. By reducing the excitation voltage to the lamp 15 by means of the voltage dividing means 24, less opposition voltage is needed. Further, the phase shift problem is eliminated thereby eliminating the need for the condenser 23.

In operation, when the line voltage is applied, the voltage divider constants are arranged so that for a lamp 15 having a firing voltage of 65 volts, for example, the voltage appearing across the transformer secondary 20 is in the order of volts, before connecting the lamp 15. The lamp 15 is essentially a constant voltage device and thus connecting it reduces the voltage to the firing voltage of 65 volts and the currents adjust themselves. As the load current is increased to induce 10 volts or greater, this potential is subtracted from the initial voltage thereby reducing it below 65 volts which causes the lamp 15 to be extinguished. This may occur, for example, at about 4 ampere-turns depending upon the transformer 21.

Continuing to increase the load current further reduces the lamp voltage in order that at approximately 22 ampere-turns, for example, the lamp voltage is substantially zero and the full line voltage appears across the resistor 25. A further increase of load current causes an increase of opposite polarity voltage until sufiicient potential is developed to reignite the lamp 15. This condition occurs at approximately 40 ampere-turns, for example.

It is preferable to select resistor values such that the differential voltage between the threshold voltage and that actually applied to the lamp is not too small so that with no load current flowing, the lamp 15 will not be extinguished in the event the line voltage drops somewhat below its normal potential.

Referring now to FIG. 3, a more versatile alternative embodiment of the present invention is shown in which the voltage dividing means 24 includes a plurality of Cir resistors which may be alternatively connected to power sources of various potentials, for example, 115 Volts or 220 volts as indicated by the legend, to make it adaptable to various power sources.

may include a plurality of transformer taps 30, 31 each associated with its respective primary windings 32, 33 and connected to respective loads, 13, 13 having predetermined current ranges as indicated by the legends. By this arrangement the current indicating device may In order to make it adaptable to a plurality of load currents, the primary winding 22.

be adapted to a plurality of power sources and to a plurality of power sources and to a plurality of load currents by merely connecting the respective power sources and loads to the proper external terminals 34, or by the requisite switching by means of switches 35, 36, and 37.

It will be appreciated, that the'power sources and loads' must be matched by means of the circuit components 'in order that the excitation voltage provided by the power source 10 is opposed by the proper opposition voltage through the transformer 21 to provide effective cancellation during normal operation.

For example, with a 115 v, 60- power source 10 and the switch 37 connected to the 115 v. terminal 34 as shown, the load 13 may be connected by switch 35 to the power source 10 as shown or the load13 may alternatively be connected to the power source 10 and the component values indicated in FIG. 3 would provide satisfactory operation in accordance with the above teaching of the present invention. With a 220 v. 60- power source 10, the switch 37 would be connected to the 220 v. terminal 34.

It will be appreciated that the excitation voltage an the load current do not necessarily have to be supplied from the same source as long as the excitation voltage is opposed by the opposition voltage to provide the effective cancellation explained above.

While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects;

What is claimed is:

1. A current indicator comprising,

(1) a transformer having a prrimary winding and a secondary winding,

(2) a glow discharge device having a predetermined ignition threshold voltage and having one electrode connected to one end of said secondary winding,

(3) an alternating current power source connected to another electrode of said glow discharge device and the other end of said secondary winding for providing sufiicient' excitation voltage to exceed said threshold, and

(4) a load connected across said power source and normally energized thereby,

(5) said load being connected in series with said primary winding of said transformer,

(6) said transformer having a turns ratio between said primary and secondary windings to provide an opposition voltage with respect to said excitation voltage to prevent ignition of said glow discharge device when said load has a normal current flowing therethrough and to permit ignition when said load has an abnormal current flowing therethrough.

2. A current indicator comprising,

(1) an alternating current power source,

(2) a glow discharge device having a predetermined ignition threshold voltage,

(3) voltagedividing means coupled across said power source, said glow discharge device being-coupled across a portion of said voltage dividing means for providing sufiicient excitation voltage to said glow discharge device to exceed said threshold,

(4) a load connected across said power source and normally energized thereby, and

(5) a transformer having its primary winding connected in series with said load and its secondary 'winding terminals connected to said glow discharge device,

. (6) said transformer having a turns ratio between said primary and secondary windings to provide an opposition voltage having a phase in opposition to said excitation voltage to prevent ignition of said glow discharge device when said load has a normal current flowing therethrough and to permit ignition when said load has an abnormal current flowing therethrough.

References Cited by the Examiner UNITED STATES PATENTS 9/1948 Duttera 340 248 4/1957 Nowogrodzki 324122 7/1963 Kelley 340 2,48 WALTER L. CARLSON, Primary Examiner. R. V..ROLINEC, Assistant Examiner. 

1. A CURRENT INDICATOR COMPRISING, (1) A TRANSFORMER HAVING A PRIMARY WINDING AND A SECONDARY WINDING, (2) A GLOW DISCHARGE DEVICE HAVING A PREDETERMINED IGNITION THRESHOLD VOLTAGE AND HAVING ONE ELECTRODE CONNECTED TO ONE END OF SAID SECONDARY WINDING, (3) AN ALTERNATING CURRENT POWER SOURCE CONNECTED TO ANOTHER ELECTRODE OF SAID GLOW DISCHARGE DEVICE AND THE OTHER END OF SAID SECONDARY WINDING FOR PROVIDING SUFFICIENT EXCITATION VOLTAGE TO EXCEED SAID THRESHOLD, AND (4) A LOAD CONNECTED ACROSS SAID POWER SOURCE AND NORMALLY ENERGIZED THEREBY, (5) SAID LOAD BEING CONNECTED IN SERIES WITH SAID PRIMARY WINDING OF SAID TRANSFORMER, (6) SAID TRANSFORMER HAVING A TURNS RATIO BETWEEN SAID PRIMARY AND SECONDARY WINDINGS TOPROVIDE AN OPPOSITION VOLTAGE WITH RESPECT TO SAID EXCITATION VOLTAGE TO PREVENT IGNITION OF SAID GOLW DISCHARGE DEVICE WHEN SAID LOAD HAS A NORMAL CURRENT FLOWING THERETHROUGH AND TO PERMIT IGNITION WHEN SAID LOAD HAS AN ABNORMAL CURRENT FLOWING THERETHROUGH. 